1. Field of the Invention
The present invention relates to a stage for placing a target object thereon when processing the target object. More specifically, the present invention relates to a stage having a side surface protection cover layer on the side surface of the stage. Still more specifically, the present invention relates to a stage having a side surface protection cover layer to set the potential of the stage to a guard potential.
2. Description of the Related Art
An example of a process of processing a target object is a semiconductor manufacturing process. The semiconductor manufacturing process includes a step of testing a plurality of semiconductor elements (to be referred to as “devices” hereinafter) formed on a wafer. FIGS. 6A and 6B show an example of a testing apparatus for practicing this testing process. A testing apparatus (e.g., a prober) 29 can include a loader chamber 21 and prober chamber 22. A cassette C storing a plurality of wafers W is arranged in the loader chamber 21. The wafers W are transported from the cassette C into the prober chamber 22 one by one. In the prober chamber 22, the electrical characteristics of the wafer W are tested.
As shown in FIGS. 6A and 6B, the loader chamber 21 can include a wafer transporting mechanism 23 and coarse positioning mechanism (to be referred to as “subchuck” hereinafter) 24. The wafer transporting mechanism 23 transports the wafers W one by one. The subchuck 24 aligns the direction of a wafer W to be transported by the wafer transporting mechanism 23.
The prober chamber 22 can include a stage 25, probe card 26, and positioning mechanism (to be referred to as “alignment mechanism” hereinafter) 27. The stage 25 moves in three-axis directions (X, Y, and Z directions) with the wafer W placed thereon, and rotates clockwise and counterclockwise in the θ directions. The probe card 26 is arranged above the stage 25. The alignment mechanism 27 aligns probes 26A of the probe card 26 and the wafer W on the stage 25 to each other.
The probe card 26 is fixed to the lower portion of a head plate 28 of the prober chamber 22. A test head T is arranged on the head plate 28. The test head T electrically connects the probe card 26 to a tester.
Assume that the electrical characteristics of devices formed on the wafer W are to be tested. The wafer transporting mechanism 23 extracts the wafer W from the cassette C, and places it on the stage 25 in the prober chamber 22. While the wafer transporting mechanism 23 transports the wafer W, the wafer W is aligned with a predetermined direction on the subchuck 24. In the prober chamber 22, the stage 25 is moved in the X, Y, and θ directions under alignment information from the alignment mechanism 27. Hence, the wafer W and probes 26A are aligned. The stage 25 moves in the X and Y directions to position the first device immediately under the probes 26A. After that, the stage 25 moves upward in a Z direction to bring the probes 26A into electrical contact with the electrodes of the device. The stage 25 is further overdriven, and the electrical characteristics of the device are tested. After the test, the stage 25 moves downward, and moves in the X and Y directions. By this movement, the wafer W is fed by index driving, and a device as the next testing target is arranged immediately below the probes. The stage 25 moves upward and is overdriven. The next device is tested in this state. The above steps are repeated so that the electrical characteristics of a plurality of devices formed on the wafer W can be tested.
After the test for the devices is ended, the wafer transporting mechanism 23 returns the wafer W to the initial position in the cassette C. The above operation is repeated to test the electrical characteristics of the devices formed on the next wafer W.
In a case wherein a small current flowing through a target object is to be measured by using a parametric tester or the like, a measurement accuracy of several pA or less is required. For this purpose, for example, the main body and tester may be connected through a triaxial cable or the like. A lower surface electrode or the like may be arranged on the lower portion of the stage, so that the potential of the lower portion becomes a guard potential.
By taking these measures, a current can be prevented from flowing from the frame ground (FG) or other potentials into the stage, or flowing out from the stage.
For example, in the next-generation semiconductor device, however, a current much smaller than the present current in a gate oxide film which is on the level of the tunnel current must be detected. Consequently, an influence caused by a small current due to the presence of dust or dirt and furthermore a humidity change, which are not presently considered as major problems become unignorable. When an ionic material such as dust or dirt attaches to the insulator of the stage main body, a voltage is generated by the same voltage generating principle as in a cell. This may be one of the reasons that generate the voltage. When the humidity increases, ion mobility increases, further promoting this phenomenon. Hence, the necessity of anti-dust or anti-dirt countermeasures is recognized.
Patent reference 1 discloses a probe station for performing low-current, low-voltage measurement of a wafer or other electronic test devices with a high accuracy. The probe station includes an environmental control surrounding body and peripheral conductive member. The environmental control surrounding body electromagnetically shields a chuck assembly. The peripheral conductive member is arranged around the chuck assembly element at a predetermined gap.
Patent reference 1 does not specifically explain the role of the peripheral conductive member. Still, the peripheral conducive member may be designed to serve as an electromagnetic shield, in the same manner as the environmental control surrounding body. The peripheral conductive member is arranged around the chuck assembly element at a predetermined gap from it. Therefore, although the peripheral conductive member can serve as the electromagnetic shield, it cannot block dust or dirt entering the gap from attaching to the side surface of the chuck assembly.
[Patent Reference 1]
Jpn. Pat. Appln. KOKAI Publication No. 6-53293